Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

A contest will consist of n questions, each of which is to [#permalink]

Show Tags

21 Nov 2007, 16:13

1

This post received KUDOS

11

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

25% (medium)

Question Stats:

72% (01:55) correct
28% (01:24) wrong based on 363 sessions

HideShow timer Statistics

A contest will consist of n questions, each of which is to be answered either "True" or "False." Anyone who answers all n questions correctly will be a winner. What is the least value of n for which the probability is less than 1/1000 that a person who randomly guesses the answer to each question will be winner?

A contest will consist of n questions, each of which is to be answered either "True" or "False." Anyone who answers all n questions correctly will be a winner. What is the least value of n for which the probability is less than 1/1000 that a person who randomly guesses the answer to each question will be winner?

interesting tarek, this is GMAT Prep 2 question. I got this question as 37th question me too got it wrong but then Probability has never been my strong point but still it is interesting cause got this '15 sec'. question on 37th number though I scored 760 in Prep2.

Re: A contest will consist of n questions, each of which is to [#permalink]

Show Tags

11 Sep 2013, 10:42

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________

A contest will consist of n questions, each of which is to be answered either "True" or "False." Anyone who answers all n questions correctly will be a winner. What is the least value of n for which the probability is less than 1/1000 that a person who randomly guesses the answer to each question will be winner?

A. 5 B. 10 C. 50 D. 100 E. 1000

The probability to randomly guess the answer for 1 question is 1/2, for 2 questions 1/2*1/2=1/2^2, similarly for n questions the probability is 1/2^n.

We need to find the least value of \(n\) for which \(\frac{1}{2^n}<\frac{1}{1,000}\) --> \(2^n>1,000\) --> \(n_{min}=10\).

A contest will consist of n questions, each of which is to be answered either "True" or "False." Anyone who answers all n questions correctly will be a winner. What is the least value of n for which the probability is less than 1/1000 that a person who randomly guesses the answer to each question will be winner? a) 5 b) 10 c) 50 d) 100 e) 1000

Answer Choice B

In all there are n questions, and each question can be answered 2 ways (i.e. True or False). So we will get \(2^n\) different sequences of answers. Of which one sequence is TTTTTTTT......n times (i.e. All correct Answers)

We are told that The person who get all the answers correct that means who get the sequence mentioned above (TTTTT.... n times) will be a winner.

A person can choose any sequence from \(2^n\) sequences. He has to choose TTTT.... n times in order to win the game.

So Probability that a person will win the game is \(\frac{1}{2^n}\)

What is the least value of n for which the probability is less than 1/1000 -------> \(\frac{1}{2^n} < \frac{1}{1000}\) -----------------------> Here we can cross multiply the inequality since we know that \(2^n\) will always be positive (We know that n can neither be zero nor be Negative)

So We have that \(2^n > 1000\) --------> Using n=10 we get \(1024 > 1000\) Sufficient. _________________

This is the kickoff for my 2016-2017 application season. After a summer of introspect and debate I have decided to relaunch my b-school application journey. Why would anyone want...

Check out this awesome article about Anderson on Poets Quants, http://poetsandquants.com/2015/01/02/uclas-anderson-school-morphs-into-a-friendly-tech-hub/ . Anderson is a great place! Sorry for the lack of updates recently. I...